AT&T has confirmed a data breach but there are yet many unknown details. The telecom giant said it recently learned that three employees of one of its vendors accessed some of its accounts without proper authorization. AT&T did not disclose the number of accounts or what information was breached.

"This is completely counter to the way we require our vendors to conduct business," AT&T said in a published statement. "We know our customers count on us and those who support our business to act with integrity and trust, and we take that very seriously. We have taken steps to help prevent this from happening again, notified affected customers, and reported this matter to law enforcement."

An undisclosed number of call records and Social Security Numbers were accessed sometime between April 9 and April 21, AT&T confirmed. The accounts were accessed as "part of an effort to request codes from AT&T that are used to 'unlock' AT&T phones in the secondary mobile phone market," the company said.

Customers can request that phones be unlocked once they have fulfilled their wireless contract. AT&T believes the aim of the breach was to spoof customer identities in order to unlock phones, which are worth more on the secondhand market.

Accounting for Shades of Gray

We caught up with Alberto Solino, a technical program manager at security software and services firm Core Security, to get his take on the breach. He told us this is another example of companies failing to understand the risks that come along with third-party access -- and facing a crisis that may have been prevented by proactively seeking out or understanding potential attack paths.

"You can't make assumptions when it comes to security," Solino said. "You have to find these attack paths and validate them before someone else does or your business and most critical assets will always be at risk."

Andy Rappaport, chief architect at Core Security, told us privileged partners are in a gray area between insiders and outsiders. Security enforcement, network access, identity- and access-management entitlements, and auditing must account for these shades of gray.

Rappaport said he understands that business efficiency thrives on efficient supply-chains and federated partnerships. Security and access control are necessary to allow speed, he said, just like cars ultimately need brakes in order to safely travel fast.

"A company's attack surface grows as an exponent of the reliance on partners, outsourcing and even Software-as-a-Service," Rappaport said. "They are relying on not only their security policy and enforcement, but also on their partner's. It stretches the trust boundaries beyond the enterprise."

Preventing Partner Misbehavior

Jon Rudolph, senior software engineer at Core Security, said AT&T's statement indicated the company could not or did not sufficiently limit the partner access to its data. As Rudolph sees it, AT&T is talking about the behavior of the partner when it should be talking about how this information was exposed in the first place.

"Is this about requiring partner behavior or preventing partner misbehavior? If we're talking about security, it's the latter," he said, noting it's possible that customer identity was a necessary vector in getting the phones unlocked. "Are companies thinking about what attack paths are possible through the identities in their business? In this case, it sounds like the downstream effect of getting the unlock codes was a privacy breach."

Rudolph concluded that it's valuable for enterprises to see events like this coming so they can stay one step ahead. Three trusted individuals allegedly looking to make some money, and potentially hundreds of customers affected as a side effect, he said, and this should matter to companies.